The present invention relates to fluid power motors in general, and more particularly to improvements in gear type motors. Still more particularly, the invention relates to external type motors.
Heretofore known fluid power motors which utilize external spur, herringbone or helical gears are of simple construction and can be manufactured at a relatively low cost. However, they exhibit the drawback that the RPM of the output member is invariably high. This severely limits their utility, i.e., such motors cannot be employed for transmission of high torque at relatively low speeds because they would have to be combined with complex reducing gears which would contribute excessively to the overall cost of the prime mover assembly.
It is also known to provide a gear type fluid power motor with an internal gear and an external gear which rolls along the teeth of the internal gear and thereby performs an orbital movement about the axis of the output shaft. Such motors can operate at low speeds but their cost is very high, especially at a high output torque. Moreover, the regulation of fluid flow into and from such motors is quite complex which results in a significant increase of the initial and maintenance cost.